1. Field of the Invention
The present invention relates generally to crashworthy aircraft seats, and in particular, to crashworthy aircraft seats with variable energy attenuation.
2. Description of Related Art
Crashworthy aircraft seats have been around for some time. The first such seats were designed for pilots, but soon after, crashworthy seats for other passengers, such as military troops, began to appear. These crashworthy seats are most often used in aircraft that take off and land vertically, such as helicopters, tilt rotor aircraft, and other rotary wing aircraft. These type of aircraft are more susceptible to vertical hard landings and crashes. The purpose of crashworthy aircraft seats is to eliminate unnecessary injuries and fatalities in relatively mild impacts and minimize injuries and fatalities in severe survivable mishaps.
For typical crashworthy aircraft seats, the weight of a seat portion, the passenger, and the passenger""s gear combine to create a xe2x80x9cstroking load.xe2x80x9d In a hard landing or crash, the stroking load moves downward over a certain xe2x80x9cstroke distancexe2x80x9d relative to a support structure of the crashworthy seat. The goal of the crashworthy seat is to absorb and attenuate the kinetic energy of the stroking load as it moves over the stroking distance, thereby transferring the kinetic energy away from the passenger. Because the human spine can only withstand limited compressive forces, inadequate energy absorption by a crashworthy aircraft seat during a hard landing or crash can result in serious spinal injury or death.
There are many factors that the affect the weight of passengers or troops in a crashworthy aircraft seat, including: whether the troop is male or female, the troop""s weight percentile, and whether the troop is equipped with gear or not. As one might expect, crashworthy aircraft seats are frequently used by passengers and troops for which these factors vary widely. For example, an unequipped female troop in the 5th weight percentile weighs about 110 pounds, while a fully equipped male troop in the 95th weight percentile weighs about 241 pounds. Anthropometric data on male and female troops is widely available.
Most crashworthy aircraft seats involve a seat assembly that slides relative to a frame assembly in the event of a hard or crash landing, referred to herein as a xe2x80x9ccrash pulse.xe2x80x9d Although various means are used to attenuate the kinetic energy of such landings, the energy attenuation means generally fall into one of four categories: (1) hydraulic or pneumatic cylinders; (2) tube deformers or splitters; (3) metal shavers; or (4) wire deformers or benders. Although some crashworthy aircraft seats have means of adjusting the energy attenuation according to the size of the passenger or occupant, none provide variable energy attenuation during a single crash pulse or crash event.
The first category of crashworthy aircraft seats, those that include hydraulic or pneumatic cylinders to attenuate energy, usually involve complicated linkages to which the cylinders are coupled. An example of such a device is the aircraft seat disclosed in U.S. Pat. No. 5,558,301 issued to Kerdoncuff et al. In the Kerdoncuff et al. seat, as the passenger sits down in a non-pivoting seat, the weight of the passenger causes the orientation of the linkage to change, resulting in a proportionate change in energy absorption during a crash pulse. The energy absorption of these types of devices are adjustable, but not variable. In other words, the initial energy absorption setting may be adjusted, but it does not vary during a single hard landing or crash pulse.
The second category of crashworthy aircraft seats, those that include tube deformers or splitters, usually involve tubes that are deformed one or more times by one or more dies as a seat assembly slides relative to a frame assembly during a crash pulse. Examples of such devices include U.S. Pat. No. 4,997,233 and U.S. Pat. No. 5,273,240, both issued to Sharon. In the Sharon seats, as a seat assembly slides relative to a frame assembly, tubular members are forced through one or more dies that deform the tubular members. Although the latter device allows for self adjustment of the energy absorption, neither of these devices exhibit variable energy attenuation during a single crash episode or crash pulse.
The third category of crashworthy aircraft seats, those involving metal shavers, is exemplified by U.S. Pat. No. 5,842,669 issued to Ruff. In the Ruff seat, as a non-pivoting seat assembly slides relative to a frame assembly, elongated members are shaved, or planed, by cutting elements, thereby absorbing energy during a crash pulse. Such shaving devices do not provide for variable energy attenuation during a single crash landing or crash pulse.
The forth category of crashworthy aircraft seats, those that deform or twist wires to absorb energy, involve plastically deforming one or more wires by drawing, twisting or bending. An example of a wire twisting device is U.S. Pat. No. 4,408,738 issued to Mazelsky. An example of a wire drawing device is U.S. Pat. No. 4,523,730 issued to Martin. In the Mazelsky seat, as a non-pivoting seat assembly moves relative to a frame assembly during a crash pulse, wires coiled around telescoping tubes are plastically twisted, thereby absorbing energy. In the Martin seat, as a non-pivoting seat assembly slides relative to a frame assembly, wires are drawn through dies and deformed, thereby absorbing energy. Neither of these devices allow for variable energy attenuation during a single hard landing or crash pulse.
For these reasons, it is clear that although significant strides have been made in the crashworthy aircraft seat industry, significant shortcomings remain.
Because the developments in the area of crashworthy aircraft seats have not adequately addressed the issue of variable energy attenuation, there is a need for a crashworthy aircraft seat that can absorb or attenuate the energy of a single crash pulse at a variable rate, regardless of the weight of the passenger in the seat. Prior-art crashworthy aircraft seats are not capable of variable energy attenuation during a single hard landing or crash pulse.
Therefore, it is an object of the present invention to provide a crashworthy aircraft seat that can absorb or attenuate the energy from a hard landing or crash at a variable rate during the crash pulse.
It is another object of the present invention to provide a crashworthy seat for an aircraft which can absorb or attenuate the energy from hard or crash landings at a variable rate, wherein the crashworthy seat has a quick release means so that the crashworthy seat can be quickly and completely removed from the aircraft.
It is another object of the present invention to provide a crashworthy seat for an aircraft which can absorb or attenuate the energy from hard or crash landings at a variable rate, wherein the crashworthy seat is mounted entirely to an aircraft bulkhead so that damage to the aircraft floor or ceiling does not affect the operation of the crashworthy seat.
It is another object of the present invention to provide a crashworthy seat for an aircraft which can absorb or attenuate the energy from hard or crash landings at a variable rate, wherein the energy is attenuated by a variable energy attenuating device including a wire bending apparatus and a plastically deformable wire having a non-uniform transverse cross-sectional geometry along the length of the wire.
It is another object of the present invention to provide a crashworthy seat for an aircraft which can absorb or attenuate the energy from hard or crash landings at a variable rate, wherein the energy is attenuated by a variable energy attenuating device including a wire bending apparatus and a plastically deformable wire having a non-uniform transverse cross-sectional geometry along the length of the wire, and the wire is restrained and plastically deformed multiple times in a zig-zag fashion to prevent the crashworthy seat from rebounding back upward after the downward stroke in which the energy from a crash is attenuated.
These objects are achieved by providing a crashworthy seat for an aircraft having a support structure coupled to the aircraft, the support structure including an upper portion and a lower portion. A seat assembly having a plurality of upright members is slidingly associated with the support structure. A guide means is coupled to the support structure for guiding the upright members as the seat assembly slides relative to the support structure. A variable energy attenuating device for plastically deforming a wire is coupled to the seat assembly. The plastically deformable wire passes through the variable energy attenuating device, but is coupled at one end to the upper portion of the support structure, and at the other end to the lower portion of the support structure. The wire has a selected transverse cross-sectional area that is non-uniform over its length. As the seat assembly slides relative to the support structure, the wire is plastically deformed by the variable energy attenuating device, whereby the kinetic energy of the sliding seat assembly is attenuated at a selected variable rate by the plastic deformation of the wire as the seat assembly slides relative to the support structure. The seat assembly remains in a static start position during normal operation and slides into an end position only during hard landings or crash events.
The plastically deformable wire has a non-uniform cross-sectional geometry selected to produce a predetermined relationship between stroking distance and stroking load. The selected cross-sectional geometry allows the crashworthy seat to accommodate a wide range of loads without the need for complicated weight detection devices or manual adjustment devices. The wire is restrained and plastically deformed multiple times in a zig-zag fashion. This prevents the crashworthy seat from rebounding back upward after the downward stroke in which the energy from a crash is attenuated. The seat is mounted to an aircraft bulkhead to allow the seat to function properly should the aircraft floor or ceiling be deformed during a crash. The seat is mounted with quick release pins to allow for quick and complete removal of the seat from the aircraft.
The present invention provides significant advantages. Primarily, the crashworthy aircraft seat of the present invention provides variable energy attenuation during a single crash event or crash pulse. In the present invention, a wire having a non-uniform cross-sectional geometry along its length is plastically deformed to attenuate the energy of a hard landing or crash. By selectively varying the cross-sectional geometry of the wire, it is possible for a single crashworthy aircraft seat to accommodate a wide range of passengers. For example, the seat of the present invention can accommodate and protect a wide range of military troops, from an unequipped female in the 5th weight percentile, or about 110 pounds, to a fully equipped male in the 95th weight percentile, or about 241 pounds. Protection in this range is accomplished, for the first time, without the need for complicated weight detection devices, or manual adjustment devices. The passenger does not have to estimate the weight of himself and his gear. Nor does the passenger have to manually adjust the energy attenuation value. The non-uniform cross-sectional geometry of the deformable wire is selected to produce a predetermined relationship between stroking distance and stroking load over a wide range of loads without the need for any manual adjustment.
These and other objects and advantages of the present invention will be apparent in the following detailed description when read in conjunction with the accompanying drawings.